Apparatus for controlling environmental conditions, suitable for use underwater

ABSTRACT

The subject of the invention described in the following specification relates to the problem of maintaining a safely breathable oxygen-containing atmosphere. Thus, the invention is especially useable under abnormal environmental conditions where it is necessary to provide and control an atmosphere suitable therein. The disclosed illustrative embodiment is a selfcontained closed circuit-type underwater breathing apparatus for diver use. A plurality of oxygen sensor cells, preferably at least three, each thermistor temperature compensated, are exposed to the gas stream in the system, each providing a current resulting in voltage drop across the thermistor, directly related to oxygen concentration which voltages then are amplified and electronically processed to operate oxygen supply means, which is a solenoid valve, whereby oxygen partial pressure is constantly maintained within a predetermined range. In the processing, the amplified voltages are electronically mathematically averaged and processed to deliver a single control signal to the solenoid. The system is adjusted at atmospheric pressure to provide one-half atmosphere oxygen partial pressure at a selected voltage level, e.g. about 2.4 volts average amplified cell voltage. As the quantity of oxygen thereafter varies in use by the diver, the average voltage varies linearly and the solenoid acts responsively thereto. Each amplified cell output is also connected into an alarm circuitry so that should any cell (or two or more) provide a voltage corresponding to oxygen partial pressure below or above a predetermined safe oxygen range, an audible alarm is sounded as a warning that something is wrong in the system. Separate visual oxygen partial pressure indicators are connected into the circuitry at the electronic amplification stages so that the diver may observe the individual indications provided by each of the sensor cells and, thereupon, determine the emergency remedial steps necessary to be taken. In the exemplary three-sensor system, the probability of simultaneous or close timewise malfunctioning of more than one sensor or its directly associated circuitry is extremely low - so low that in practical use it may reasonably be taken as zero. Consequently, the diver, while of course, recognizing the remote possibility of such a plural maloccurrence, may, and in practice will, presume any two similar partial pressure indicators correctly to reflect the actual internal conditions of the system - unless, of course, his own understanding of the particular situation might rarely permit a different conclusion. Contemplating most importantly such a single maloccurrence (thereupon resulting in an alarm sounding and indications from the meters that one of the voltage inputs is spurious) the design of the system, involving as it does the aspect of solenoid valve control by the average voltage, is such that the electronic circuitry responds to limit, or stabilize, the effect of the spurious voltage input upon the average voltage. This is accomplished via transistor clipping circuitry and an associated regulated pg,3 voltage source. Thereupon a nonvarying voltage, which is not outside the selected range for acceptable and safe oxygen partial pressure, constantly appears in the average voltage. Accordingly, the effective average voltage is then within the safe range aNd continues effectively to operate and to maintain a suitable oxygen partial pressure as long as the signals from the remaining cells are developed and delivered and they themselves are a correct measure of the oxygen partial pressure actually in the system. The system contemplates also an adjunctive, separate and exteriorly attachable sensor-indicator means by which the system may be further verified whereby the security of the diver is much enhanced. The system includes inert gas supply means which may be manually or automatically operated for supplying the remaining gas volume and pressure necessary for breathing underwater. By these and other means, the safety for the diver is enormously increased and the purpose of his dive can be accomplished under a minimum of constraint.

United States Patent John W. Kanwisher Box 53, Woods Hole, Mass. 02543;Walter A. Starch I1, Box 592 Big Pine Key,

[72] Inventors 2.33043 21 AppLNo. 780,961 221 Filed Dec.4,l968

[45] Patented Jan. 19, 1971 [54] APPARATUS FOR CONTROLLING ENVIRONMENTALCONDITIONS, SUITABLE FOR [56] References Cited UNITED STATES PATENTS2,830,583 4/1958 Finney 128/142 3,410,778 11/1968 Krasberg 204/1953,252,458 5/1966 Krasberg 128/147 3,370,457 2/1968 Lemm 73/27 PrimaryExaminer-Richard A. Gaudet Assistant Examiner-G. F. DunneAttorney-Stevens, Davis, Miller & Mosher ABSTRACT: The subject of theinvention described in the following specification relates to theproblem of maintaining a safely breathable oxygen-containing atmosphere.Thus, the invention is especially useable under abnormal environmentalconditions where it is necessary to provide and control an atmospheresuitable therein. The disclosed illustrative embodiment is aself-contained closed circuit-type underwater breathing apparatus fordiver use. A plurality of oxygen sensor cells, preferably at leastthree, each thermistor temperature compensated, are exposed to the gasstream in the system, each providing a current resulting in voltage dropacross the thermistor, directly related to oxygen concentration whichvoltages then are amplified and electronically processed to operateoxygen supply means, which is a solenoid valve, whereby oxygen partialpressure isconstantly maintained within a predetermined range. In theprocessing, the amplified voltages are electronically mathematicallyaveraged and processed to deliver a single control signal to thesolenoid.

The system is adjusted at atmospheric pressure to provide one-halfatmosphere oxygen partial pressure at a selected voltage level, e.g.about 2.4 volts average amplified cell voltage. As the quantity ofoxygen thereafter varies in use by the diver, the average voltage varieslinearly and the solenoid acts responsively thereto. Each amplified celloutput is also connected into an alarm circuitry so that should any cell(or two or more) provide a voltage corresponding to oxygen partialpressure below or above a predetermined safe oxygen range, an audiblealarm is sounded as a warning that something is wrong in the system.Separate visual oxygen partial pressure indicators are connected intothe circuitry at the electronic amplification stages so that the divermay observe the individual indications provided by each of the sensorcells and, thereupon, determine the emergency remedial steps necessaryto be taken. In the exemplary three-sensor system, the probability ofsimultaneous or close timewise malfunctioning of more than one sensor orits directly associated circuitry is extremely low so low that inpractical use it may reasonably be taken as zero. Consequently, thediver, while of course, recognizing the remote possibility of such aplural maloccurrence, may, and in practice will, presume any two similarpartial pressure indicators correctly to reflect the actual internalconditions of the system unless, of course, his own understanding of theparticular situation might rarely permit a different conclusion.Contemplating most importantly such a single maloccurrence (thereuponresulting in an alarm sounding and indications from the meters that oneof the voltage inputs is spurious) the design of the system, involvingas it does the aspect of solenoid valve control by the average voltage,is

. sucli that the electronic circuitry responds to limit, or stabilize,the effect of the spurious voltage input upon the average voltage. Thisis accomplished via transistor clipping circuitry and "anassociatedregulated voltage source. Thereupon a nonvarying voltage, which is notoutside the selected range for acceptable and safe oxygen partialpressure, constantly appears in the average voltage. Accordingly, theeffective average voltage is then within the safe range and continueseffectively to operate and to maintain a suitable oxygen partialpressure as long as the signals from the remaining cells are developedand delivered and they themselves are a correct measure of the oxygenpartial pressure actually in the system. The system contemplates also anadjunctive, separate and exteriorly attachable sensor-indicator means bywhich the system may be further verified whereby the security of thediver is much enhanced. The system includes inert gas supply means whichmay be manually or automatically operated for supplying the remaininggas volume and pressure necessary for breathing underwater. By these andother means, the safety for the diver is enormously increased and thepurpose of his dive can be accomplished under a minimum of constraint.

P TENI EB JAN 19 1911 UC T m OXYGEN FROM PRESSURE REGULATOR VALVE-44C.54 MOUTH PIECE-2Q FROM OXYGEN FROM MA U L VE- INVENTOHS OHN W.KANWISIHER, ALTER A. STARCK, 11

CONTROL VAL APPARATUS FOR CONTROLLING ENVIRONMENTAL CONDITIONS, SUITABLEFOR USE UNDERWATER .This invention relates to apparatus andmethods formaintaining a safelybreathable atmosphere, and most especially so underconditions which are not normal to human life. The invention isparticularly advantageous in the underwater environment, such as inmaintaining a constantly safe oxygen level in deep sea chambers anddiver breathing equipment. Broadly considered, however, the inventionfinds application also in space apparatus and, as will appear, ininstance under ordinary atmosphericpressure conditions. Further,although the invention is'especially advantageously applicable to theprotection of human life, it is applicable in the maintenance of asuitable atmosphere or other critical condition regardless of the objectof protectionor'theconditiondesired to be maintained. i

The invention in structure and modes of operation is exemplified hereinby illustrating and describing underwater breathing apparatus of theself-contained closed circuit type, recently, and now more prominently,coming into use by divers. The invention is especially useful forrelatively deep diving but it is equally adapted for shallow water.

Generally described, and as revealed by the prior art, the closedcircuit type of diving equipment involves inhalation and exhalationwithin the confines of the equipment. Thus, normally none of the gasesare discharged from the equipment except on ascent, when it is necessaryto release internal pressure. Known units, suchas shown in U.S. Pat. No3,252,458, include a carbon dioxide absorber, thru which the gasatmosphere is passed on inhalation or exhalation, the oxygen level beingconstantly monitored and replenished up to a predetermined level. Aswill be understood, therefore, this type of system is highly desirablebecause no oxygen is wasted on exhalation, and the diluent gas, usually(costly) helium in deep water, is completely conserved. Consequently,longer period underwaterventures are readily feasible and at very greatsaving in cost of helium.

The aforementioned U.S. Pat. No. 3,252,458 is believed to constitute themost closely allied description of apparatus relative to the presentinvention. This prior teaching Before an oxygen deviceof the classdisclosed in U.S. Pat. No. 3,000,805. The sensing device as used inactual oxygen concentration determination is, or may be, technicallydescribed diver interrelationa polarographic cell. The cell ispositioned in the gas stream for contact therewith following the carbondioxide elimination stage. The cell operates to deliver a minuteelectric signal varying with the concentration of oxygen in the stream,oxygen actually penetrating into the cell and effecting a flow ofcurrent according to its partial pressure. The electric signal thusdeveloped is utilized by associated electric circuitry to operate oxygeninput means whereby the diver is supplied with additional oxygen fromthe oxygen tank as needed.

The aforesaid U.S. Pat. No. 3,252,458 constitutes a substantial advancein the art of underwater breathing. Asis well knownto those involved inthis art, the ventures of divers in- .volve extreme dangersto life; andeven where death may be avoided, serious physiological impairment mayresult during a necessary but too rapid decompression. The aforesaidpolarized cell, being an extremely rapid responder to oxygen, andaffording thereupon a constant and reliable output signal, has renderedbreathing apparatus of the type under consideration far more feasible.However, the hazards are so great as to command the greatest possibledegree of certainty of continuously perfect suitability to the needs ofthe diver as they suddenly develop underwater; otherwise underwatertechnological advances will be seriously hampered by refusal of peopleto work in the art. In other words, practicalities considered, theultimate in possible safely is needed. To this end, quality in componentparts is essential and it is of prime importance that the entire systemfunction properly as an assembly. Even though such be provided, failuresin any equipment must be recognized as inevitable.

Serious failures are minimized to an extremely high degree by thepresent invention and such asmay possibly occur in using this inventionare reduced to a level of substantially zero criticality. This is incontrast to the prior levels of achievement of other workers whichleaves much to be desired. As aforesaid the teaching of the prior artare notable and it is not intended unduly to speak disparagingly ofthem. However, the prior art stopped seriously short of the desirableunderwater safety standards in a number of respects, and it must bepointed out the known teachings and equipment expose the diver toextremely dangerous conditions in the event of a particular type ofelectronic and/or associated equipment failure. Unfortunatelysuchequipment failure is inherently possible and quite likely to occurespecially in the course of use of equipment over a long period of time.This particular fault will be described more fully in relation to thepresent invention; however, a few brief comments at this point willserve to bring the matter to sharp focus absent surrounding shroudingcomplexities of other many details.

In considering this, it may be well first to recall that a percentoxygen atmosphere can well be fatal to a diver in deep water, e.g. 100feet even if breathed for only a very short time. and that lower oxygenpartial pressures are equally or more dangerous particularly as thebreathing time is longer or more rapid due to activity. Therefore,anysystem wherein oxygen partial pressure can rise beyond safe limitsmust provide against the occurrence of an over-oxygenated atmosphere byall possible means if it is to fulfill the safety demands of a systemuseful beyond the critical depth for pure or high partial pressureoxygen breathing. The system. of the prior U. S. Pat. No 3,252,458includes an electronic circuitry designed to maintain oxygen at a levelselected by the diver. In this respect, the circuitry is well conceivedand the occurrence of too much oxygen would not ordinarily be expectedto happen under proper operating conditions of the equipment. However,as suggested above, it is again repeated that it is to be expected, infact forecasted, in providing any equipment for prior art, are subjectto at least two types of critical failures.

The first is obvious, namely an occurrence involving an instantaneouscessation in the current flow such that it becomes immediately apparentto the diver, that all of the control equipment is for some reasontotally inoperative and that emergency procedures are necessary to beemployed. This type of situation is indeed very serious and the divercan be in grave danger, especially at considerable depth; but this is asituation which heretofore in general has been taken into account andemergency procedures have been established whereby the diver mostprobablywill be able to reach the surface. However, some of the priorproposals are themselves a serious danger. For example, one approach isto supply a continuous flow of oxygen at about the minimum needed forbreathing, the minimum oxygen flow being independent of the electronicmetering system which supplies a selected additional optimum quantity.Thus, the diver can theoretically make his way to the surface withoutharm. However, providing the same minimum flow at all depths, requires acomplex mass flow regulator which is prone to malfunction and does nottake into account the fact that physiological requirements for oxygenmay vary by a factor to 10 depending upon diver activity. The minimumflow approach is thus inherently pron-e to dangerous over or underoxygenation depending upon activity and minimal flow selected.

As aforesaid, this type of electronic failure involves a complete andinstantaneous failure in the system whereby the metering means does notdeliver oxygen in the predetermined desirable quantity. However, thereis another type of failure, evidently not perceived by the prior workersin the art, such being of a less apparent and more subtle nature notinvolving instantaneous inaction of the metering system or circuitry.

The fault in this instance involves a slow degradation from properfunction as for example in the sensing unit or amplification section, inthe course of which the system continues to operate, but imperfectly.This may be described as a malfunction and, though not common, doesoccur. lf, for example, the malfunction occurs in the sensing cell, oramplification circuitry, it will effect delivery of excess orinsufficient oxygen (depending upon whether the signal output decreasesor increases), the remaining equipment functioning normally, theatmosphere will shortly become over-or underoxygenated. Moreover, allindications from the equipment will read normal since the system willadd or fail to add oxygen in whatever quantity is required to hold thesignal output at the predetermined level, i.e., meters will show theoxygen content to be at, or reasonably near the proper level, alarmswill not sound, and the diver will not be warned. The result can easilymean death to the diver from oxygen poisoning or anoxia unless a codiveris alert and observes abnormal behavior on the part of the endangeredman. if such good fortune prevails, emergency procedure which may forexample involve interchange of the breathing mouthpiece between diverscan be employed while proceeding to the surface in a predeterminedorderly manner, i.e., in view of decompression requirements.

Within the limits or reasonably feasible precautionary measures, and itbeing indisputable that absolute safety can only be approached and neverquite reached, the present invention enhances the inherent safeness ofthe breathing system by such magnitude that the hazard of over orunderoxygenation as a matter of probability due to equipment failurebecomes substantially nonexistent.

Before proceeding to other attributes of the invention, which are ofsubstantially of the same order of enhancement over known equipment, itis thought to be desirable to discuss the necessity of diverinterrelation and/or interfunction with the breathing equipment. Suchdiscussion follows in the succeeding paragraphs.

lnsofar as is known, no attempts have as a practical matter beensuccessful in interrelating diver equipment with a measurable bodyfunction in order that the diver may be warned directly of possibleimpending unconsciousness following equipment failure or malfunction.Therefore, in the use of presently available equipment, the diver mustvisually observe indicators and heed audible signals in order to protecthimself in the event of equipment failure. Prior devices, particularly,for example, that according to U.S. Pat. No. 3,252,458 requiressubstantially continuous noting of the operating state of the system.Likewise, the present invention involves diver meter observance andattention to warning. However, the present invention goes far beyondprior provisions for warnings and, more importantly, the presentinvention provides the diver with actual analytical knowledge of thestate of the system to an extent and of a kind far transcending theprior art. Although the diver is required to note and act upon theavailable information provided by the invention herein, his failure todo so for an extended period of time is not likely, by the very greatestprobability, to leave him in serious circumstances. Stated in anotherway, though it is quite desirable for a diver to observe the state ofthe equipment every minute or so, the present invention affords such ahigh degree of protection against internal equipment a malfunction thatthe diver is provided with a very great margin for human failure.

The abstract of the invention will have provided an introductory amountof understanding of the present invention such that upon reflection inthe course of considering the foregoing discussion, the basis forindicating the remarkable advancesmay be well appreciated.

Referring further to devices as known to the prior art, it should beapparent that where a single oxygen monitoring unit is employed, itbeing coupled with an electronic indication related to oxygenconcentration, the diver can never at any time be certain of the actualoxygen concentration in the system. If, for example, the alarm circuitrywere to be involved in a failure in the system, the oxygen concentrationmight be dangerously out of line even though the indicating meterindicated a normal and safe breathing atmosphere. The diver is entirelyat the mercy of the equipment and any suspect indication must be takenas an emergency.

ln overcoming the disadvantages referred to above in equipment of theclosed circuit, self-contained type, and in related types ofapplications where oxygen concentration is critical or to be controlled,the present invention preferably employs three oxygen sensing ormonitoring units, such being of the general type disclosed in U.S. Pat.No. 3,000,805, As aforesaid, these monitoring units, or cells provide aminute voltage which is proportional to oxygen concentration, thevoltage varying accordingly with such concentration. The output of thecells being extremely small, three separate amplification sections areprovided, each amplifying the signal from its respective signal source,that is, each cell respectively. Each amplified signal is measuredthrough an isolating resistor by a microammeter which is scaled fromzero to 100, the full scales being linearly representative of oxygenpartial pressure of from about zero to about one atmosphere, individualcell outputs of from zero to about 5 volts, (morerealistically about 4.7volts in a practical operating circuit.) corresponding to the partialpressure scale. Accordingly, an amplified cell output of approximately2.4 volts (practical embodiment, about 2.35 corresponds to approximately0.5 atmospheres oxygen partial pressure.

The three signals are further processed by electronic circuitry wherebyan average voltage is obtained which is thereafter processed to operatea solenoid oxygen input valve. The solenoid valve is set to deliveroxygen at times when the average amplified voltage falls below about 2.4volts. Thus. the system normally operates to fulfill one of its intendedobjects, that is the provision of an oxygen concentration ofapproximately 05 atmosphere in the system. Under normal operatingconditions it is not usual that the oxygen concentration would risesignificantly above 0.5 atmosphere, since the supplied oxygen isconstantly depleted by the diver in breathing. However, in normaloperations of the equipment the solenoid valve remains closed when theaverage voltage rises to or above about 2.4 volts.

The system includes audible alarm circuitry deriving a signal from eachof the amplified cell voltages. The alarm is electronically set to givewarning if any one cell voltage falls below about 1.9 volts or risesabove about 3.3 volts. The said range of 1.9 volts to 3.3 volts will beseen to correspond approximately to about 0.4 and about 0.7 atmospheresoxygen partial pressure, thus providing a range for tolerable oxygenconcentration and safe breathing by the diver.

Although the present invention contemplates still further and highlyimportant features tending to insure the safely of the diver, it ispointed out that the association of equipment described immediatelyabove affords the diver several advantages in that the three independentsignal provide him with intelligence which when coupled with his basicknowledge of the characteristics of the system enable him to reachconclusions concerning the probable state of the equipment that is notpermitted by one signal, or even two signals. As will be understood, andas indicated above, a single signal affords little reliable evidence.Two signals at variance with each other merely leaves the diver in aquandry as to which signal is the correct one. Three signals, however,enable him to compare two against one and consider the intelligence as amatter of probability. The probability of two sensors being in error is,of course, the square of the probability of one being in error, and thatprobability decreases with decreasing time; hence the probability of twosensors malfunctioning or failing at the same time is substantiallyzero. Since the system will also function within safe limits on only twosensors, the same high probability of safe operation applies to theoxygen control signal. Additionally, the three signals provide a moreaccurate measure of the oxygen concentration in the respect that theaverage of the three signal tends to compensate for internal componentvariation from indicated values. As is well known,

electronic components are true to their rated values on the basis ofplus or minus about percent, plus or minus 5 percent in highly selectcomponents. Internal inaccuracy of this type is compensated for inproportion to the number of separate signals processed through theelectronic averaging means. In this respect it should be apparent thateven two monitoring and amplification stages provide improvement inaccuracy of the final applied signal. It may be mentioned in thisconnection, that this invention provides means in the electronic systemserving as an adjustment upon each amplified monitoring output whereby,in the main, such internal inaccuracies are compensated for.

Further. however. the preferredembodiment of this invention includesadditional electronic circuitry whereby any one or all of the amplifiedvoltages is clipped" or held at about L9 and 3.3 volts should it fall orrise to those limits. This clipping prevents an erroneous signal frompulling the average voltage, and hence oxygen concentration outside ofsafe limits. Inthis way the system continues to function reliably solong as the remaining two oxygen monitor signal are a reliable orcorrect measure of the actual oxygen concentration in the system. Thus,in the present system where three monitors are employed; one of them maybe effectively eliminated and the remaining cells or monitor signals asamplified and averaged with the clipped output of the erroneous sensorwill continue to deliver oxygen within the established range, and,moreover,

such remaining monitor signals areeffective continuously to provide theoxygen concentration at near the optimum of about 0.5 atmosphere.

The audible alarm sounds at the time of voltage clipping; therefore, thediver is made aware of the questionable functioning of the equipment,although he may have noted a disturbing condition theretofore byobservation of the partial pressure indicators.

The invention further contemplates the use of a separate oxygen partialpressure indicator, the same being self contained and powered, and beingprovided with a microammeter reading in terms of oxygen partial pressureas the other meters of the main system. Such additional partial pressureindicator is contemplated as being constructed entirely electricallysimilarly to the monitor cells, the amplification circuitry and theindicator circuitry of the main equipment. Being entirelyself-contained, however, it is contemplated that such unit maybeemployed either in combination with the main equipment. being adaptedto probe the internal oxygen atmosphere thereof and respond to providecorroboration of any or all partial pressure indicators in the mainsystem, or, it being useable in the event of failure of two sensors oreven total failure of the main equipment whereby manual oxygen feed maybe accomplished with knowledge of the concentration as afforded by theadditional unit.

As was pointed out in the abstract presented at the forepart of thisspecification, the present invention proceeds from the point of viewthat in the continual usage of the equipment the probability ofsimultaneous failure of two signals in any possible respect isconsidered tobe substantially zero. This conclusion is notonly a matterof mathematics but it is based upon the facts that such equipment iscontemplated as being constructed'of very high quality components andassembly quality control'being of the highest, both facts being inconsideration of the extreme hazards that are involved in underwaterwork and the desire to enhance the base factors involved in the timeprobability calculation. Moreover, in use the equipment is cardcarefully checked and partly renewedbefore each dive. Nonetheless,superimposed upon this concept is the realization that one of two ormore signal system may fail due to its own characteristic and that uponsuch happening if the equipment is;thereafter to be realisticallyuseable by the diver, the system must provide him with means fordetermining with substantially equal certainty which signal of anassembly of signals is in error. This is accomplished by providing atleast three informative signals. The above-mentioned probabilityconsiderationsare effectively meaningful in a diver system involvingthree signals, the diver observing the indications of two like signalshaving the high probability of correctness, and comfortably relyingthereon in conducting himself in the emergency situation.

It should be appreciated that the advantages of the time probabilityfactor as embodied in the present invention are extremely great;however, the invention proceeds beyond such point and, in the preferredembodiment, provides automatically for the continued operation of theequipment based upon the two remaining signals without the need for anyattention whatsoever on the part of the diver. Considering theimportance of surely providing for a minimum oxygen concentration andagainst amounts above a predetermined maximum oxygen concentration atall times, the: feature of automatic operation to continue concentrationwithin the limitation is regarded as quite important in .that there isno time delay involved in adjusting the equipment when a signal is atvariance with the true concentration present in the system. The presentsystem relieves the diver completely of :any concern regarding thereliability of the system insofar as oxygen content is concerned. and heis free to start his ascent to the surface at once without the necessityof making adjustment; and notably important, in an unalarmed mentalstate. Further, highly important is the fact that even' though the alarmshould fail to sound at the proper point, the probability of diversafety is not signiftcantly lessened. This is because of the fact thatthe probability of a second failure before surfacing is extremely low;moreover (in following standard diving procedure.) the diver will havevisually noted a failure and will have aborted the dive long before timeunder water admits of a second failure.

It is recognized that modifications of the basic approach to the systempreferred herein are possible. For example, a two signal systemsupplemented by an exterior probe sensor-indicator affords substantialpossibilities for increased information and safety. Yet, in such case,precious manipulative time is involved. Thus, it is believed thatdeviations from a system including at least three signals, coupled withautomatic continued safe operation following the loss of one, is verydifficult, if not impossible, to justify in view of the safety hazardthat is involved. Where inanimate subjects are regulated in accordancewith the teachings of this invention, it is recognized that somerelaxing of strict adherence 'to the approach of the ultimate inreliability and operation may be justified.

Various other aspects of the invention will appear as the discussionthereof continues hereinafter. The invention is illustrated by drawingsappended hereto; they being directed to the specific embodiment asillustrative of the invention.

In thedrawings:

FIG. 1 is a plan view of the described embodiment showing the variousparts in relative position;

FIG. 2 is a vertical sectional view thru a portion of FIG. I whereinvarious parts may be seen in greater detail;

FIG. 3 is a sectional view of an oxygen detection or sensing meansemployed in each of three monitoring stages of FIG. 4; and

FIG. 4 is a circuit diagram of the electrical monitor-control system.

Referring to FIG. 1 of the drawings, the entire apparatus is shown inthe form of a layout showing the positioning and relationship of thevarious parts. FIG. 2 may simultaneously be considered. In the drawingsnumeral 10 refers to a tank for pressurized oxygen and numeral 12 refersto a tank for pressurized helium, or other inert gas. Since theapparatus is of the closed circuit type, the system contains a carbondioxide abon inhalation, numeral 26 denotes a conduit leading to thebreathing bag 18 and numeral 28 denotes a conduit leading off of conduit26 through which inhaled gas passes into the carbon dioxide absorbingzone before being drawn through conduit 24 to the mouthpiece. Numerals30 and 32 denote check valves for controlling the direction of flow ofthe gases upon inhalation and exhalation. As will be observed checkvalve 30 is designed to open upon inhalation and at the same time, checkvalve 32 closes, so that gases are drawn from the breathing bag throughthe absorbent canister to the mouthpiece. Upon exhalation, valve 32opens to permit the passage of exhaled gas into the breathing bag, valve30 closing simultaneously. All of the foregoing parts are well known instructure and function and do not require further detailed description.

Numeral 34 denotes an isolated portion of canister 14 which portion maybe described as a chamber of the apparatus for containing the means forinjecting oxygen into the system and the means for monitoring or sensingthe oxygen content of the circulating gases. Chamber 34 is in directfluid communication with the carbon dioxide absorber, as may be seenupon reference to FIG. 2 via a perforated plate or screen there shown atnumeral 35. As will be seen, conduit 24 connects into chamber 34. Also,as will be seen, tube 28 connects into conduit 36, (see FIG. 2,) thelatter directing the gases to the extreme end of the carbon dioxideabsorber where it enters chamber 38, from which it passes reversely intoand through the absorbent via perforated divider plate 39, more clearlyseen in H0. 2, upon inhalation. Chamber 38 is merely a section of theoverall canister 14, the plates being therein to form a zone forretaining the carbon dioxide absorbent. Inhalation then continues todraw the gas mixture then deluded of carbon dioxide, through theabsorbent into chamber 34 where its oxygen content is monitored, andfrom chamber 34 the gas mixture passes through conduit 24 to the divervia the connecting mouthpiece. Thus, the circuitry includes the passageof the gas from the breathing bag on inhalation through the circuitryleading to the carbon dioxide absorber and rebreathing of the exhaledgas, it being drawn through the absorber via conduit 24, the gas in itspassage being treated for carbon dioxide removal, and having its oxygensupply replenished as necessary.

Oxygen replenishing takes place in chamber 34. As will be observed, theoxygen supply is connected to a solenoid operated valve 40 mountedwithin chamber 34, oxygen line 42 providing for delivery of oxygen fromthe tank via the regulator 44c. Line 42 connects to the oxygen supplytank via manually operable valve assembly 44 which valve is open whenthe system is in use and closed when it is not.

Replenishment of oxygen occurs as the quantity of oxygen in the systemlowers following its usage by the lungs and subsequent conversion tocarbon dioxide. The gas mixture in the system is continuously monitoredfor oxygen content in chamber 34 as it flows therethrough. Themonitoring is accomplished by a plurality of polarographic electrolyticcells, numeral 46 which vary their voltage output according to theoxygen content of the gas mixture. The plural assembly of the cells willbe described in greater detail at a later point herein. In general,however, it may be mentioned at this point that each individual cellcontains a liquid electrolyte which absorbs oxygen from the gas streamacross a membrane. Thus, the high the partial pressure of oxygen in thegas mixture the greater will be the amount of oxygen absorbed by thecells. Conversely lesser oxygen partial pressure results in a smalleroxygen absorption. As aforesaid, the output of each cell varies withabsorbed oxygen, output being greater with higher oxygen content andless with smaller oxygen content.

The output of each cell is delivered to an electronic processing systemdenoted generally by numeral 48, this system being housed, together withbatteries, in separable chamber 49. The resulting signal from theelectronic processing is employed as a control for the solenoid valve40. The monitor and control system is designed and electricallyproportioned to maintain the oxygen supply as nearly constant aspossible, as related to a predetermined desirably oxygen partialpressure in the gas mixture. A more complete discussion of this aspectof the invention in relation to desirable physiological conditions, theelectronic circuitry and the related cells, will appear hereinafter.Before proceeding with such further discussion it is desirable tocomplete a general description of the overall assembly.

The helium supply tank 12 is connected to chamber 38 via line 50. Line50 connects into a valve assembly 52. Valve 52b is manually operable andserves to add helium to the gas mixture by the divers manipulation inresponse to decreasing volume (deflation) of the breathing bag. As willbe understood, so long as the exterior pressure resulting from the depthof the water remains constant, the gas volume in the system normallywill remain constantfHowever, as the diver descends, pressure increasesand the pressure increase is reflected by a deflation of the breathingbag. The volume required for full inhalation is resupplied when valve52b is opened, whereby helium is admitted is in sufficient quantity tobring the volume of gas in the breathing circuitry back up to the properlevel. Similarly, upon ascent the internal pressure must be relieved.Such release of pressure is readily accomplished by breathing outwardlyaround the mouthpiece or thru the nose, or a relief valve may beemployed in the system. It will be understood that the helium volume maybe automatically supplied in response to internal demands. For example.this may be accomplished by a demand regulator of any well known type.

Numeral denotes a oxygen content indicator assembly which serves toinform the diver of the oxygen content of the stream as reflected by thecells. The metering assembly will be more fully described at a laterpoint but it may nowbe stated that it includes 3 meters, i.e., aseparate meter for each cell, thereby separately reflecting thecondition of each one of them. The indication is provided constantly andthis assembly permits the diver to know immediately of deviations ofeach cell from its expected normal output as well as any change inoxygen partial pressure as indicated by all of the meters. The indicatorassembly connects into the circuitry via leads 62.

Since the oxygen supply at all times is absolutely critical, oxygen tankI0 is provided with a bypass line 64 leading into chamber 38, throughwhich line oxygen supply may be manually delivered by a valve 44b. Aswill be understood, such valve is normally closed and oxygen would notpass through this line except under emergency conditions, or when usingpure oxygen for decompression at shallow depths.

Referring again to FIG. 2, it will be seen that separable chamber 49,the canister section 14, and enclosing endplates 65 and 66 are held inassembled relationship by rod 68 which threads into one endplate througha waterproof gland in the other endplate thus tying the entire assemblytogether. The spring 70 seen in chamber 38 serves to hold the orificeplate 72 in position thereby to maintain the absorbent material withinthe desired zone.

The relatively thick member denoted by numeral 74 seen between chambers34 and 49 serves a number of purposes including the sealing of chamber34, forming an endplate for chamber 49, an assembly base for cells units46, solenoid valve assembly 40, the electric circuitry 48, batteries ofwhich there are several later to be specified and a base for attachingand passing external lines such as 42 and 62 into the interior. As willbe seen, the walls of chamber 49 are merely as provided by a cylindricalor tubular section seen denoted at numeral 76.

Numeral 78 denotes a switching member passing thru the wall 76 therebyenabling the exterior actuation of switch unit 80 within chamber 49.

It may be pointed out that member 74, positioned and serving asdescribed affords significant advantages when it is necessary to serviceany component of the unit. This becomes apparent in noting that all ofthe sensing and control equipment is removable and, so removed, is heldas a single assembly upon the member 74. The only attachment of themember to the device as a whole is then by way of oxygen line 42, whichis easily detached. Further, a malfunctioning assembly may quickly andeasily be replaced by setting a new assembly in position.

Further, the manner of assembly and provision ofchambers affords theadvantage that additional chambers may be added, e.g. similar to and inthe manner in which chamber 49 is provided. For example, it may bedesirable to attach special communication module and as will be apparentsuch may easily done. The canister-chamber units and endplates arefitted tightly and are rendered watertight as by sealing O-rings.gaskets, such as at numeral 92. Of course, all fittings attaching to theassembly are similarly made watertight. The materials employed in theconstruction of thecanister-chamber assembly may be as desired; howeverclear plastic such as Lucite is quite satisfactory and offers theadvantage of visual inspection for moisture and absorbent conditionwhile diving.

The material employed for carbon dioxide removal is well known, it beingsold trade name Barylyme, and being composed mainly of barium hydroxidewhich absorbs" by reacting to form barium carbonate. An indicating colorchange is incorportated to indicate when its absorbing capacity isexhausted. A

Referring to FIG. 1, the tanks and canister-chamber section areassociated together by releasable metal band 82. The tanks and canisterchamber section are separated by nesting blocks 84 which conform to thecontour of the parts. Harness straps, as for example denoted by numeral86, anchored in blocks 84 serve to hold the apparatus securely to thediver. The breathing bag 18 attaches to the harness via twist studswhich are mounted on the harness and lock into the breathing bag at theshoulders and lower corners 90. The breathing bag may be of materials asdesired; however clear flexible plastic such as vinyl is satisfactoryand offers the advantage of visual inspection for water inside the bag.A small plug 18A provides a drain for removal of water resultingfromcondensation or leakage around the mouthpiece.

The mouthpiece, 20 is provided with a valve 94 serving to open and closethe breathing circuit as and when desired.

Since the gas cylinders are under high pressure, needle valves areemployed as a means to permit a controlled flow without experiencingheavy blasts into the equipment. Thus, valves 44b and 52b include such,and the orifice 96 for gas discharge from the solenoid valve 40 is of atype permitting flow regulation. Ideally the discharge from the solenoidvalve is adjusted so that it overrides the control point by l to percentof an atmosphere, thus it is activated for only about 3 seconds every 15to seconds and requires minimal drain on the batteries.

Numeral 98 denotes a oxygen pressure indicator providing neededinformation on oxygen supply level. A similar pressure indicator may beprovided for the helium tank.

Numeral 100 denotes the alarm which suitably is fixed to member 74,being connected into the circuitry as in FIG. 4.

A solenoid-valve assembly of highest efficiency is desirable in orderthat the lowest power drain will be made upon the batteries. Allowingthe inner plunger maximum travel produces greatest useable power.Accordingly, the same valve spring may be opened with less batter drain,allowing the use of smaller batteries. Plural solenoids and/or valvesmay be employed, either as standbys or they may be in tandem. operatingfull time in order to increase reliability.

A dessicant may be provided in the system in order to take up moisturefrom the diver s breath.

, FlG. 3 illustrates the construction of the oxygen sensing meansemployed in the invention, the same being more fully iscussedhereinafter in association with the electrical circuitry. In thisdrawing numeral 110 (numeral 208 of monitor stage 200. FIG. 4)designates the type of operatingcell of monitor stages 200, 201 and 202depicted in FIG. 4. including inner electrode 112 and outer surroundingcylindrical electrode 114 (for example, numerals 209 and 210 of FIG. 4)which may suitably be respectively of platinum and silver, the

latter having a thin coating of silver oxide thereon. The electrodes,being mounted concentrically, are separated by any suitable insulatingmaterial. e.g. a plastic mass denoted by numeral 116. Leads 118 and 120serve to connect the device into the electronic circuitry as seen inPK]. 4. The thermistor 207 seen in FIG. 4, (not shown in FIG. 3b, may bemounted on the sensor retaining member 122 or may be cast in the base116 of the electrode assembly itself so as to be in the same temperatureenvironment as the sensing means itself. Retaining member 122 is simplya sheet or bar ofany suitable material. e.g., acrylic plastic. bearing atapered hole 126 into which the electrode assembly is inserted in themanner of a stopper. it acts only as a holder for the electrodeassembly. Numeral 46 of FIG. 1 indicates such a holder with three holesfor the three separate electrode assemblies. Numeral 130 denotes aliquid electrolyte. for example, potassium hydroxide, the same beingcontained between the electrodes in a shallow circular channel formed bythe electrodes extending beyond the insulating mass 116.

Numeral 134 denotes a oxygen-permeable membrane which may be ofpolyethylene or any suitable material. As will be seen, the membranefits tightly downwardly over the electrode and serves also to retain theelectrolyte. Numeral 136 denotes an outer membrane-retaining memberhaving a passageway 138 whereby the membrane is left exposed to theoxygen atmosphere while being securely held in a fixed position. Themembrane retaining member is of any suitable material, e.g., siliconerubber.

As aforesaid, the cell(s) herein employed are entirely similar indesign, operation and function to the cells described in prior US. Pat.No. 3,000,805; and the disclosure of said patent is hereby made a partof this specification. It may be noted that the herein described cellprovides a shallow channel for holding potassium hydroxide, or similaracting material. rather than the fabric disc as in the patent. Thus, thegeneral type of cell being well known, further discussion does notappear to be necessary.

Since the oxygen sensor cells operate to develop signals in themicroampere range, and since the electronic circuitry is highlysensitive, it is important that the electrodes be as free of impuritiesas possible.

Referring now to FIG. 4, there is disclosed an illustrative embodimentof the electronic circuit of the present invention including threeoxygen monitoring stages 200, 201 and 202. As shown, the threemonitoring stages are energized from a suitable direct voltage'so'urce,illustrated as a single battery 203, via single-pole double-throw switch204. Switch 204 is ganged with other switches as will be made clearhereinafter. Each stage may be energized by separate batteries inpractice so that failure of a single battery will not disable all of themonitoring stages.

The first monitoring stage 200 includes a voltage divider consisting ofresistors 205 and 206 connected across battery 203 via switch 204 shownin a closed position. The voltage divider may be constructed as apotentiometer having a fixed or movable tap if desired. Connected inparallel with resistor 206 is temperature compensating thermistor 207and oxygen sensing electrolytic cell 208 connected iri series. Cell 208includes a reference electrode 209 made of silver or other suitablematerial, having a thin film of an oxide or other suitable material onthe surface thereof and a reaction electrode 210 made of platinum. Thecell includes an electrolyte, such as potassium chloride or potassiumhydrpxide, between electrodes 209 and 210 as seen in FIG. 3. It is knownthat the current flow through electrolytic cells of the type used isproportional to the concentration of oxygen to which the cell issubjected. it is known that the current flow through electrolytic cellsof the nature of cell 208 is temperature dependent, and it is desirablethat temperature compensation be provided. Thermistor 207 has asubstantially equal but opposite temperature coefficient to that of cell208. lnoperation, the thermistor 208 is desirably so placed that it willhave the same temperature as that of the gaseous mixture being sensed.The

current provided through cell 208 causes a voltage drop acrossthermistor 207. The output from monitoring stage 200 is taken acrossthermistor 207 and appears as a positive voltage on lead 211 connectedto one side of thermistor 207. The other side of thermistor 207 isconnected to ground.

Oxygen monitoring stages 201 and 202 are constructed in the same fashionas oxygen monitoring stage 200, and are likewise energized from battery203 via switch 204. Monitoring stage 201 includes a voltage dividerconsisting of resistors 212 and 213 connected across battery 203 viaswitch 204. A series connected thermistor 214 and oxygen sensing cell215 are connected in parallel with resistor 213. Electrode arrangement215 includes a silver reference electrode 216 and a platinum reactionelectrode 217. The output from monitoring stage 201 is taken acrossthermistor 214 and appears as a positive voltage on lead 218 connectedto one side of thermistor 214, the other side of thermistor 214 beingconnected to ground. Oxygen monitoring stage 202 includes a voltagedivider consisting of resistor 219 and resistor 220 connected acrossbattery 203 via switch 204. A series connected thermistor 221 and oxygensensing cell 222 are connected in parallel with resistor 220. Oxygensensing cell 222 includes silver reference electrode 223 and platinumreaction elec trode 224. The output from monitoring stage 202 is takenacross thermistor 221 and appears as a positive voltage on lead 324connected to one side of thermistor 221, the other side of thermistor221 being connected to ground.

The three distinct voltage outputs from the three oxygen monitoringstages are fed via leads 211, 218 and 324 to signalprocessing amplifiers225,226 and 227, respectively. The details of signal-processingamplifier 225 are shown. Signal processing amplifiers 226 and 227,illustrated as boxes, are constructed identically to signal-processingamplifier 225.

Signal-processing amplifier 225 includes a directly coupled linearoperational amplifier 228 and a signal-clipping stage 229. The signaldeveloped across thermistor 207 is fed via line 211 to the positiveinput terminal 230 of directly coupled linear operational amplifier 228.The operational amplifier is provided with a ground terminal and anegative input terminal 236. The positive input terminal 230 ofamplifier 228 is connected to ground via capacitor 231. Numeral 232denotes the amplifier output terminal. A negative feedback path isprovided from the output terminal 232 to the negative input terminal 236of the operational amplifier 228. The negative feedback path includesgain control variable resistor 233 and fixed resistor 234 connected inseries. A resistor 235 is connected between ground and the negativeterminal 236 of the operational amplifier 228. The operational amplifier228 may be advantageously constructed as an integrated circuit, andshould have sufficient gain so that its output is from zero to aboutvolts. A possible gain of about 100 is desirable. A variable resistor237 is connected to appropriate terminals of the operational amplifier228 or forms a part thereof for zero setting the operational amplifier228. The output from terminal 232 of the operational amplifier 228appears at point A which is connected via isolating resistor 238 toground through microammeter 239. lsolating resistor 238 is preferablylarge enough so that even were microammeter 239 or the leads theretoshorted, the voltage at point A would not be significantly changed. Theoutput from terminal 232 is also connected to point E via resistor 240.Point E is connected via resistor 241 to the negative input terminal 242of a directly coupled averaging amplifier 243. The positive inputterminal 244 of averaging amplifier 243 is connected via resistor 245 toa positive 2.4 -volt terminal 294 of regulated power supply 295. Theregulated power supply 295, which will be described in detail below,further includes a negative 6.75-volt terminal 296, a positive 6.75-voltterminal 297, and a ground terminal 298.

Point E, the junction between resistors 240 and 241 is also coupled tosignal-clipping stage 229 which includes two normally nonconductivetransistors 247 and 252. Point E is connected directly to the emitterelectrode 246 of normally nonconductive NPN transistor 247. Thecollector electrode 248 of transistor 247 is connected to the positive6.75-volt terminal 297 of regulated power supple 295 via resistor 249.The junction between collector 248 and resistor 249 is designated pointB. Point E is also connected via germanium diode 250 to the emitterelectrode 251 of normally nonconductive PNP transistor 252. Thecollector electrode 253 of transistor 252 is connected to the negative6.75-volt terminal 296 of the regulated power supply 295 via resistor254. The junction between collector 253 and resistor 254 is designatedpoint C. The base electrodes 255 and 256 of transistors 252 and 247,respectively, are connected to the positive 2.4-volt terminal 294 of theregulated power supply 295. The transistors 247 and 252 havebase-emitter characteristics such that the base-emitter path becomes aconductive whenever about one-half a volt appears between the base andemitter electrodes. The characteristic of germanium diode 250 is suchthat is becomes conductive in a forward direction whenever about 0.4volt appears between its plate and cathode.

Signal-processing amplifiers 226 and 227 are constructed identically tosignal-processing amplifier 225 described above, and will not beseparately described in detail. The points corresponding to point A,point B, point C and point E are shown for signal-processing amplifier226 as points A, B, C, and E; respectively, and for thesignal-processing amplifier 227 as points A", B, C" and E",respectively. As can be seen, points B, B and B are connected together,and points C, C and C" are connected together, The base terminals ofnormally nonconductive NPN and PNP transistors in signalprocessingamplifier 226 and in signal-processing amplifier 227, which correspondto transistor 247 and transistor 252 of amplifier 225 are alsoconnected, via leads 311 and 312 respectively, to the positive 2.4-voltterminal 294 of regulated power supply 295. Point A of signal-processingamplifier 226 is connected to ground via series connected largeisolating resistor 255 and microammeter 256. Isolating resistor 255 is alarge resistor, and serves the same function as resistor 238 mentionedabove. Terminal A" of signal-processing amplifier 227 is connected toground via series connected large isolating resistor 257 andmicroammeter 258. Isolating resistor 257 also is a large resistor, andserves the same function as resistor 238 mentioned above. Point E, atwhich the output from signalprocessing amplifier 226 appears, isconnected via resistor 259 to the negative terminal 242 of directlycoupled averaging amplifier 243. Point E, at which the output fromsignalprocessing amplifier 227 appears, is connected via resistor 260 tothe negative input terminal 242 of directly coupled averaging amplifier243. Resistors 241, 259 and 260 are the same size. The output of directcurrent averaging amplifier 243, an operational amplifier, appears atpoint D which is connected via resistor 261 to the base terminal 262 ofnormally nonconductive NPN transistor 263. The emitter terminal 264 oftransistor 263 is connected to ground. The collector terminal 265 oftransistor 263 is connected to the positive 6.75- volt terminal 297 ofthe regulated power supply 295 via resistor 266. The collector electrode265 is also connected via resistor 267 to the base electrode 268 ofnormally nonconductive PNP transistor 269. The emitter electrode 270 oftransistor 269 is connected to the positive terminal of battery 271. Thecollector terminal 272 of transistor 269 is connected to the negativeterminal of battery 271 via series connected single-pole double-throwswitch 273 and the oxygen control solenoid 40.

As mentioned above, the collectors of the signal-clipping transistors247 and 252 are coupled respectively to the positive 6.75-volt terminal297 and the negative 6.75-volt terminal 296 of the regulated powersupply 295 via resistors 249 and 254 as are the collectors ofcorresponding transistors, which are not shown, but form a part ofsignal-processing amplifiers 226 and 227. Points B, B and B are alsoconnected to a first input line 275 of alarm circuit 276. Line 275 isconnected via resistor 277 to the base electrode 278 of normallynonconductive PNP transistor 279. The collector electrode 280 oftransistor 279 is connected to one terminal of audible alarm 281. Theother terminal of audible alarm 281 is connected via single-poledouble-throw switch 282 to the negative terminal 296 of power supply295. The collector 280 is also connected to the collector electrode 286of normally nonconductive PNP transistor 285 which has its emitterelectrode 287 connected to the positive 6.75-volt terminal 297 of theregulated power supply 295. The positive 6.75-volt terminal 297 ofregulated power supply 295 is connected via series connected resistors288 and 289 to the base electrode 390 of transistor 285. The junctionbetween resistors 288 and 289 is connected to the collector electrode290 of normally nonconductive NPN transistor 291, The emitter electrode292 of transistor 291 is connected to the negative 6.75-voltterminal'296 of the regulated power supply 295. The base electrode 293of transistor 291 is connected to point C of signal-processing amplifier225 and points C' and C" of signal-processing amplifiers 226 and 227.

The regulated power supply 295 includes a battery pack consisting offour 9-volt batteries 299, 300, 301 and 302. Batteries 299 and 300 areconnected in series through single-pole double-throw switch 303 topositive 6.75-volt terminal 297 via resistor 304. Resistor 305 and a 2.4volt Zener diode 306 are connected between terminal 297 and groundterminal 298. The positive 2.4-volt terminal is provide at the junctionbetween Zener diode 306 and resistor 305. Connected in series betweenthe positive 6.75-volt terminal 297 and the negative 6.75-volt terminal296 is series connected resistor 309 and the collector emitter path ofNPN transistor 310. The base electrode of transistor 310 is connected tothe positive 6.75- volt terminal 207 via series connected 6.25-voltZener diode 308 and 6.75-volt Zener diode 207. Switches 204, 282, 273and 303 are preferably ganged together so as to simplify operation ofthe circuit. While all of the switches are shown as single-poledouble-throw switches, only switch 303 serves to connect differentelements into the circuit. In the position shown in the drawing, switch303 connects series connected batteries 299 and 300 to the regulatingpart of power supply 295. In such a position series-connected batteries301 and 302 are held in reserve. in the event battery 299 or battery 300fails or becomes too low in voltage, switch 303 is used to switch tofresh reserve batteries 301 and 302.

in a practical embodiment of the illustrated circuit of the presentinvention, the valves and identification of components used are asfollows:

Resistor 205. soon Variable resistor 238 -50Kn. Resistor 206. 1, 0000Resistor 212. 5600 Variable resistor 227 0-50Kn. Resistor 218. 1,0000Operational am liner 200.. 'I-52 Philbriok. Resistor 210. 5000 Averagingamp er 248. 'I-02 Philbriok. Resistor 220. 1, 0000 Resistor 284. 0K0Capacitor 281 ut. Resistor 288. 471m Transistor 247 2N 3003. Resistor240. 6 8K0 Transistor 252 2N 8905. Resistor 241. 211m Transistor 263..2N B008. Resistor 245. mm Transistor 269.. 2N 1860. Resistor 240. 271mTransistor 279 2N 2038. Resistor 254. 27Kn Transistor 286 BM 8088Resistor 255.. 47K0 Transistor 291 2N 390B. Resistor 257. 47KnTransistor 310.. 2N 0 Resistor 259. mm Zener diode 306 2. 4 volts.Resistor 260. 27KB Zener diode 307 6. 75 volts. Resistor 201. 211m Zenerdiode 308..... 6. 25 volts. Resistor 266. ooxn Resistor 267- 2 7K0Resistor 277. 211m Resistor 288. 100Kn Resistor 289. 211m The matter ofzero setting and calibrating the illustrative circuit of the presentinvention will now be described. Microarnmeters 239, 256 and 258 have ascale from O-lOOp 'amperes. Full scale deflection is chosento'correspond to one is supplied to oxygen sensing cell 208 so that nooxygen approvides no current representing the presence of oxygen and nooutput representing the presence of oxygen appears across thermistor207. Zero setting variable resistor 237 associated with operationalamplifier 228 is adjusted so that meter 239 reads zero, indicating theabsence of oxygen between electrodes 209 and 210. In a similar fashion,an oxygen free gas, such as propane, is supplied to electrodearrangements 215 and 222 so that no oxygen appears between electrodes216 and 217 nor between electrodes 223 and 224. Under thesecircumstances, no output representing the presence of oxygen appearsacross thermistor 214 and thermistor 221. Zero setting variableresistors, not shown, associated with directly coupled operationalamplifiers, not shown, within signalprocessing amplifiers 226 and 227are adjusted, in the same manner as variable resistor 237, so thatmicroammeters 256 and 258 also read zero indicating the absence ofoxygen between electrodes 216 and 217 and between electrodes 223 and224. After microammeters 239, 256 and 258 have been zero set,oxygen-sensing cells 208,215 and 222 are placed in a gaseousenvironment, such as air, containing approximately 20 percent oxygen atatmospheric pressure. Positive going outputs appear across each ofthermistors 207, 214 and 221 which are representative of the presence ofa gas containing 20 percent oxygen by volume at atmospheric pressurebetween electrodes 209 and 210, electrodes 216 and 217, and electrodes223 and 224, respectively. The positive-going outputs are fed to theinputs of signal-processing amplifiers 225, 226 and 227, respectively.The gain of directly coupled operational amplifier 228 is adjusted byvarying the value of variable resistor 233 in its negative feedbackpath. increasing the value of resistor 233 reduces the amount ofnegative feedback and increases the gain of operational amplifier 228.Decreasing the value of resistor 233 increases the amount of negativefeedback and decreases the gain of operational amplifier 228. The gainis adjusted until microammeter 239 deflects to 20 20 percent of fullscale. When so set, the 20 percent deflection represents an oxygenconcentration corresponding to a partial pressure of 0.2 atmospheressupplied to oxygen'sensing cell 208. Since operational amplifier 228 isa linear amplifier, half scale deflection would represent aconcentration of oxygen corresponding to 0.5 atmosphere supplied tosensing cell 208.

in a similar manner, gain control resistors, not shown, associated withdirectly coupled operational amplifiers, not shown, withinsignal-processing amplifiers 226 and 227 are adjusted so thatmicroammeters 256 and 258 deflect to 20 percent of full scale. When soset, 20 percent scale deflection on microammeters 256 and 258 representa concentration of oxygen corresponding to a partial pressure of 0.2atmospheres supplied to cells 215 and 222 respectively. Since thedirectly coupled operational amplifiers in signal-processing amplifiers225 and 226 are linear, half scale deflection on respective meters wouldrepresent a concentration of oxygen corresponding to a partial pressureof 0.5 atmosphere supplied to oxygensensing cells 215 and 222,respectively. The circuit having been calibrated and zero set, is readyfor operation.

Since the circuit has been calibrated in the manner set out above,positive voltages of approximately 4.7 volts, 1 atm.) at points A, A andA" and a full scale deflection of meters 239, 256 and 258 indicates aconcentration of oxygen corresponding to a partial pressure of 1atmosphere as determined from the outputs of oxygen sensing cells 208,215 and 222 respectively. Ideally, positive voltages of 2.35 volts atpoints A, A and A" indicates a concentration of oxygen corresponding toa partial pressure of 0.50 atmospheres as sensed by the correspondingoxygen-sensing cells. As a practical matter, positive voltages of 2.4volts at points A, A and A" indicates a concentration of oxygencorresponding to a partial pressure of approximately 0.5 atmosphere assensed by corresponding sensing cells. Positive voltages at points A'A"and A' of approximately 1.9 volts would indicate a concentration ofoxygen corresponding to a partial pressure of approximately 0.4atmosphere, while positive voltages at points A, A and A" of about 3.3would indicate an oxygen concentration corresponding to a partialpressure of approximately 0.7 atmosphere as sensed by correspondingsensing cells.

Having described the apparatus and associated circuitry, and the mannerby which it is prepared for use, its functioning in use by a diver isdescribed hereinafter. As will be appreciated, such functioning is inparticular regard to the occurrences taking place in the electroniccircuitry since the electrical system, beginning with the oxygenconcentration monitors through to the solenoid operated valve, includethe only variants. and otherwise the type of system is well understood.Of course, it will be appreciated that the oxygen monitor stages 200,201 and 202 correspond to the sensor assembly designated by numeral 46in FIGS. 1 and 2, and that the circuitry shown in FIG. 4 corresponds tothat which is shown in block form in FIGS. 1 and 2 at numeral 48. Allswitches included in the circuitry must be in the on position, namely,switches 204, 273, 282 and 303, they being ganged together in actualassembly and indicated at numeral 78. The system is to be considered asin use by a diver, i.e. dynamic, during which the oxygen supply isdepleted according to his requirements.

Each of the electrolytic oxygen sensing cells 208, 215 and 222 provide acurrent flow directly related to the concentration of oxygen in thegaseous mixture within the part of the breathing apparatus in which theyhave been incorportated. The currents provided by the electrolyticoxygen sensing cells 208, 215 and 222 flow through thermistors 207, 214and 221, respectively, causing a voltage drop across each one.

The direct voltage, which is proportional to the concentration of oxygenas sensed at stage 200 appearing across thermistor 207 is fed to theinput terminal of signal-processing amplifier 225 via lead 211, andappears across capacitor 231 connected to the positive terminal 230 ofoperational amplifier 228. An amplified output, from directly coupledoperational amplifier 228, appears at point A and is directly linearlyrelated to its input. The output from point A is fed via resistor 238 tomicroammeter 239 on which the percentage of deflection indicates theconcentration of oxygen, i.e., zero to l atmosphere, as sensed byelectrode arrangement 208.

As will be understood, the voltage outputs arising at stages 201 and 202are processed identically to that of stage 200 and are fed to theirrespective microammeters 256 and 258. Thus, three independent amplifiedvoltages directly related to oxygen partial pressure appear at points A,A and A".

The amplified positive output voltage from operational amplifier 228,appearing at point A, is coupled to point E. So long as the voltageatpoint E remains within the range of from approximately 1.9 voltspositive to approximately 3.3 volts positive corresponding to sensedoxygen partial pressure of about 0.4 atmosphere to about 0.7 atmosphere,the voltage at point A effectively appears at point E.

Referring to the voltages at points E and E", the signals incoming toprocessing amplifiers 226 and 227 are processed identically to theforegoing voltage appearance at point E. Therefore, they need not beindividually discussed.

Normal functioning of the apparatus in use by the diver sin v wels. elas?!siitat..admsfiafifjmq.E1i usually only slightly above 2,4 volts butnot above about 3.3 volts, and such voltages are processed thruoperational amplifier 243 and thereafter in a manner hereinafterdescribed to operate the oxygen input solenoid valve and effect thereplenishment of oxygen in the system in proportion to the loweredvoltage inputs following oxygen usage by the diver. Of course, normalfunctioning is expected, it is intended, and it is usual in the courseof using the equipment. However, the aspect of some abnormality in asystem of this, or any type, whereby the diver is endangered, is ofparamount interest herein. Since the final processing thru point D tothe solenoid valve is discussed at a later point, and such processing isthe same whether or not the input is normal, discussion or variationsfrom normal voltages at points E, E" and E" is presented below inrelation to the other important circuitry. Moreover, a very great amountof repetition will be possible to avoid, and

better understanding of the circuitry will be had, by a discussion ofsuch variations at this point together with their possible interpretedmeaning by the diver in observing the indicators.

in the event either on one or more of the voltages appearing at pointsE, E and E" are below or above the established range of about 1.9 voltsto about 3.3 volts, the circuitry functions to hold the voltage at thelimiting value. If only one signal voltage reaches the clipping pointthe remaining two continue to operate the system. if two or all signalvoltages should reach the clipping point, the system will not operatebut the meters may still be used as indicators for manual control solong as two continue to read similarly. The reason (or reasons) for theoccurrence is indeed important to the diver but, herein such are notnecessarily so much a matter of concern; moreover, discussion of allcasual possibilities in detail would be very extensive and also is notconsidered to be necessary. However, for example, the cause may be amalfunction of the solenoid valve such that it is on open position fulltime, or on closed position full time, or batteries may be failing. Ifit is either, switching to the reserve batteries may restore normaloperation; however, if the reserve batteries do not do so, immediatesurfacing procedure is undertaken. Since the helium supply is 10 percentoxygen, it may be employed according to known techniques from maximumdepth of the dive as the oxygen supply. The helium supply may beemployed at any less depth; but if in shallow water, e.g. 60 feet orless, damage or danger is not likely from as much as 3.0 atmosphereoxygen for the corresponding short surfacing time. Therefore, the diveris not in serious trouble even if oxygen is fed in via the bypass linedescribed hereinbefore and surfacing is gotten under way according topredetermined and diver-learned procedure. Additionally, if the problemis only in the solenoid valve, its oxygen supply may be cut off, andoxygen then fed via the bypass line manually, in which case thecircuitry will serve to supply coneentration indications.

Since fresh operational long life and similar reserve batteries arealways employed as a precaution, especially in deep dives, for example,200 feet and deeper, and/or if the time for operations at such depths isnot long, batteries are not likely to cause an emergency. Similarly, ifa malfunction in high quality solenoid valve equipment is most unusualif it is properly maintained, for example, free of dirt. Accordingly,unless the equipment is seriously damaged so as to sever electricalleads or bring about a total short circuit, all of the voltagesappearing at points E, E and E" are not likely to fall outside theintended range. One voltage might, however, (though not very likely) dueto many causes. Such an outside voltage may be termed spurious" and istreated herein in the main without regard to cause. The important pointto be noted is that by the clipping of a spurious signal, in theparticular system here described, the system continues to functionnormally the diver has been warned by the alarm and will have noted hismicroammeter oxygen indicators and unless it be quite desirable not todo so, he will begin surfacing at once. if it be quite desirable toremain submerged for a time at the working depth. the oxygen indicatorssupply him with intelligencefrom which he can make a decision inreasonable safety and with knowledge in any event that an emergencyexists and that he must proceed, if at all, with due caution andattention to his system, and his physiological reactions. His buddydiver, of course, will have been alerted.

If in observing the oxygen indicators two are indicating nearlyidentically, whereas one is at odds, it will be most reasonable on thebasis of statistical probability as hereinbefore explained to make theassumption that the one is faulty since it is not likely that one hascorrectly sensed a real danger and warned of it while two havemalfunctioned in the same way at the same time because of someunrelatedinternal fault. (As hereinbefore indicated, it is proposed asan adjunct to this invention, and as a part thereof, that a specialentirely separate oxygen concentration testing instrument be suppliedfor probing the internal oxygen system so that its measurement may becompared with the indicators of the main system,

whereby substantially absolute certainty is afforded. Such an instrumentwill be obvious as to manner of construction following the teachingsherein.)

From the foregoing it will be appreciated that an enormous number ofdifferent operational occurrence might be described in which the presentequipment is useable. Yet, its function insofar as voltage clipping andaveraging is the same. it is for the plurality of sources of informationin any case invaluable to the diver, the preservation of extendedoperability notwithstanding the statistical failure aspect of oxygenconcentration control systems, irrespective of cause or type of failure,and the very high probability of safety from oxygen poisoning or anoxiafor which the invention is especially notable.

Thus, returning to the circuitry (which should not now be more readilyappreciated as a whole and in relation to the diver,') the signalclipping at all of points E, E and E" or any one or two of them occurselectronically in the same manner via their respectivecircuitry, atwhich time the alarm circuitry is also energized. A discussion of themanner of operation of this voltage clipping circuitry is presentedbelow. A discussion relative to the point E only is provided since thecorresponding similar circuitry functions in the same manner.

In the event the voltages at point E falls to about 1.9 volts positiveindicating either an oxygen partial pressure of approximately0.4atmosphere or some maloccurrence in the system, base-emitter currentflows in normally A nonconductive transistor 247 holding point E at apotential of [.9 volts positive because of the connection of the baseelectrode 256 to the positive 2.4-volt terminal 294' of the regulatedpower supply 2951 When transistor 247 conducts, its emitter-collectorcurrent flows through resistor 249 which lowers the voltage at point Bcausing normally nonconductive transistor 279 to conduct. Theemitter-collector current of transistor 279 flows through and activatesaudible alarm device 281. In the event the voltage at point E rises toabout 3.3 volts (0.7 atm.) positive, similarly indicating either excessoxygen concentration or a maloccurrence, current flows through diode 250and baseemitter path of normally nonconductive transistor 252 holdingpoint E at a potential of 3.3 volts positive because of the connectionof the base electrode 255 to the positive 2.4-voltterminal 294 of theregulated power supply 295. Transistor 252 conducts; itsemitter-collector current flows through resistor 254 which raises thevoltage at point C causing normally nonconductive transistor 291 toconduct. The emitter-collector current of transistor 291 flows throughresistor 288 lowering the voltage on collector 290, causing normallynonconductive transistor 285 to conduct. The emitter-collector currentof transistor 286 flows through and activates audible alarm device 281.

As can be seen from the foregoing a processed voltage signal appears atpoint E which may range from about a positive 1.9 volts (representing apartial pressure of about 0.4 atmosphere) to about positive 3.3 volts(representing a partial pressure of about 0.7 atmosphere. Thus, withinthe range nientioned above, is a possible signal of positive 2.4 voltswhich represents a partial pressure of about 0.5 atmosphere.

The discussion which now follows refers to the final processing of thethree signals thru the averaging amplifier to the solenoid.

The processed voltage signal appearing at point B is coupled throughresistor 241 to thenegative input terminal 242 of averaging amplifier243 which is an operational amplifier. Similarly processed voltagesignals, which are developed in signal-processing amplifiers 226 and 227and appear at point E'Eand E" are coupled via resistors 259 and 260,respectively, to the negative input terminal 242 of averaging amplifier243. Since resistors 241, 259 and 260 are the same size, the threeprocessed signals are effectively averaged, and the average signalappears on the negative input terminal of averaging amplifier 243. Whenany one of points 8. E or E". is being held at a constant positive 1.9or 3.3 volts because of the operation of the clipping stages formingpart of respective signal processing amplifiers 225, 22 o and 227, onlythe processed signals appearing at the point or points which are notclipped will contribute to the changing of the output from averagingamplifier 243. THe clipped signal will. of course, pull the averageslightly from the correct value but this effect is small and of noconsequence physiologically.

Whenever the average signal appearing on the negative input terminal 242of averaging amplifier 243 passes below the selected control point of2.4 volts, the output from averaging amplifier 243 appearing at point Dreverses from extreme negative to positive. As the output at point Dpasses through zero and becomes positive, transistor 263 conductslowering the voltage on its collector 265 causing transistor 269 tobecome conductive. When transistor 269 conducts, its emitter-collectorcurrent flows through the oxygen control solenoid valve 40 whereby it isopened. Additional oxygen is supplied to the breathing apparatusuntilthe average signal appearing on the negative input terminal 242 ofaveraging amplifier 243 increases above 2.4 volts positive. The outputfrom averaging amplifier 243 appearing at point D reverses from extremepositive to negative. As the output at point D passes through zero andbecomes negative, and transistor 263 becomes nonconductive, the voltageon its collector 265 rises causing transistor 269 to becomenonconductive thereby interrupting current flow in solenoid 40 allowingthe oxygen supply valve to close. The cycle is constantly repeated, andadditional oxygen suppliedas needed to maintain the concentration ofoxygen in the breathing apparatus at a partial pressure near 0.5atmosphere.

Referring again to matter of preventing signal strength from risingabove or falling below certain fixed limits, herein referred to asclipping, it may be helpful to discuss the reaction of the system to thenew intelligence as such appears in use. Such discussion can hardly bemore than an approximation because it must be understood that: thesystem is in use, i.e., dynamic, and therefore the example can only betaken as real in contemplation of the system becoming static until itsreaction is complete.

As aforesaid the three voltage sources are averaged. The average inputin use, and being processed thru to point D and the solenoid 40, isabout 2.4 volts or slightly higher. if the signal of one sensor weregradually falling due to some malfunction, the oxygen concentrationwould rise due to the higher signal values required of the remaining twocorrectly functioning sensors in order to maintain the said 2.4-voltaverage. Oxygen concentration would continue to rise until the erroneoussignal was clipped at about l.9 volts at which the oxygen concentrationrequired to produce the signal strength needed from the correctlyfunctioning sensors to hold the average would be about 0.53 atmosphere.Conversely, if a malfunctioning sensor were producing a rising signalthe oxygen concentration would drop until clipping of the erroneoussignal occurred at about 3.3 volts, resulting in an oxygen concentrationof about 0.41 atmosphere.

It is thought that the manner of using the described embodiment of theinvention will be quite apparent to those skilled in the art; however,by way of assistance the following procedure is set forth which has beenfound to be satisfactory.

Considering, for example, a dive of 300 feet, the oxygen supply tankshould be pressured to approximately 2250 pounds. The inert gas tank,preferably helium and oxygen should be at a similar pressure. The carbondioxide removing material should be fresh. Preferably, all batteriesshould be replaced. The sensors are supplied with about 2 drops, 1 Nsolution of potassium hydroxide and the membrane should then bepositioned securely against potassium hydroxide loss in use. Obviously,the membrane should be free of grease etc. and undamaged. A Teflon orpolyethylene membrane of about one mil thickness is found to besuitable. They are then secured in their holding base.

the system for about 3 seconds every l5 to 20 seconds. This intermittentflow will be seen to reduce battery drain. The electric switch is turnedon and calibration of the instrument is completed as heretoforedescribed.

The parts are then assembled. Care being taken against leakage.

There then being only 20 percent oxygen operating the system, the alarmcircuitry will be sounding.

With the mouthpiece in place, the equipment is taken into the water to adepth of a few feet and the main oxygen supply valve leading to thesolenoid valve is turned on whereby the wanted oxygen begins to flowinto the system. The helium valve is then opened to start pressureequalization. With the pressure equalized the system will come toapproximately 0.5 atmosphere oxygen partial pressure under normalbreathing within about 3040 seconds. As the descent is thereaftercontinued to the established depth, helium is constantly fed in asneeded to balance the pressure. The system should be closely observedfor any sign of fault.

It will be appreciated that those utilizing the device of this inventionwill need to become thoroughly experienced with it, at which time theymay choose different courses of action in circumstances where one ormore of the indicators show oxygen partial pressure outside theestablished range. Until such experience is gained, and preferablythereafter, of course, if a warning signal is heard or one or moremeters show outside the range, the dive should be aborted at once. inany event,

cause for alarm should be the signal to switch to reserve batteries,and, even though such batteries restore normal conditions, the diveshould be aborted, since obviously the reserve batteries may cause asimilar result; however, so long as the reserve batteries-provide properoperation of the system, the system may be utilized in reaching thesurface.

Some observations from experience in use may be helpful. Should theindicators by any chance show oxygen at a too high level, for example,indicating close to the top end of the range or above, it may be thatthe bypass oxygen line is pouring oxygen into the system at a very highrate. Accordingly, it should be checked to assure that it is closed. Ifthe valve is not open, the main oxygen supply should be cut off and thesystem exhausted of gas content by compressing the breathing bag. Returnto the surface should then be by way of valving in the helium supplywhich contains percent oxygen (although this may be varied) and willsupport the needs of the diver during the ascent. in feeding in thehelium-oxygen supply, the bag should be reinfiated and the gas breatheduntil the meters show about 40, meaning an oxygen partial pressure ofabout 0.4 atmosphere. The helium mixture should be resupplied in cycles,which should occur under normal breathing about every 30 to 40 secondsor replenished with oxygen by opening the tank valve and bleeding inoxygen using the meter as a guide.

Should it occur that all meters read too low, the probability is thatthe solenoid valve is not working. Oxygen is of course then valved inmanually, the content being monitored by the partial pressureindicators.

Should all meters read zero it is apparent that the circuitry isinactive, and that the meters cannot be employed for monitoring oxygen.In such case, the helium supply is relied upon as above described. itgoes without saying that the dive program should never leave the diverwith less use-able oxygen than required for his safe return to thesurface regardless of other considerations. Calculations in this regardare well known to those skilled in the art and need not be describedherein.

While embodiments of an electronic control apparatus of the presentinvention have been described in detail, other embodiments and numerousmodifications are contemplated as being within the invention, and thescope and spirit of the claims herein.

Having described a system involving three monitoring stages, it isdesired to point out that any desired number of monitor stages may besimilarly employed. It is again pointed out that three such stagesprovide significant advantages over a single stage or two stages.especially when employed in relation to clipping circuitry, as hereindescribed, or similarly effective means for nullifying or otherwiseeliminating an unwanted signal. lt is further pointed out that clippingas herein described is not mandatory provided other means are includedin the circuitry for elimination or nullification of an unwanted signal,such means being compatible with requirements of the oxygen input means,including its actuating circuitry. For example, means may be providedeven for manual switching when the alarm sounds in order to void anunwanted signal in a three signal system.

Among the possible other embodiments, are embodiments in which theaveraged signal. developed from the plurality of processed signals fromthe plurality of signal-processing amplifiers, is directly utilized tocontrol a switching device for the valve controlling solenoid or thelike, thus. replacing the operational amplifier; however, such amplifieris highly desirable because of the steepness of slope at the zerocrossover point and the simplicity of circuitry by which such slope isprovided. Obviously the averaging amplifier may be replaced by amultivibrator.

Thus, as applied to diver breathing apparatus and similar applications,the invention extends more broadly to the provi sion of plural means fordelivering a corresponding number of signals proportional to oxygenconcentration. and means for combining said signals and thereafteremploying the resulting combined signal to operate oxygen supply meansin a manner to supply oxygen according to predetermined concentration.there also preferably being associated means for indicating the oxygenconcentration represented by each such signal and/or relevant sensiblealarm means. However, where the invention is applied in situationsinvolving the control of the environment relative to material ratherthan human or animal life, the indicator alarm provision may be replacedby operation stopping means, or such may be an added feature togetherwith the indicator and/or alarm feature. Thus, for example, where achemical process is under automatic gas control the system may beemployed to effect control while guarding against a dangerouslyexplosive mixture. From this it will be apparent that the invention isnot limited to the control of an oxygen environment; rather it isapplicable to a wide variety of operations where a condition, e.g., anitrogen atmosphere, is critical or a temperature range is critical, thesensing means being replaced by a means responsive to the condition.Additionally, the invention may be employed to monitor a fluid andcontrol a condition therein, for example, an oxygen-containingbreathable liquid.

Still more narrowly however, and as applied to oxygen concentration orotherwise, the invention preferably includes means which may be plural,for eliminating, or effectively nullifying, one or more unwantedsignals, while still leaving the oxygen supply means operable to supplyoxygen within a safely breathable range related to the usersenvironments or changing environment as such may be following signalrejection, such means preferably being electrical. Moreover, such meansmay be or involve alternate circuitry relative and responsive to themodified signal for operating the input means.

Further, it is pointed out that any suitable type of oxygen sensing ormonitoring device may be employed; and that different types, ormodification of the same type of such, may be employed within the sameoperating unit. Additionally, different types, or modified types may beemployed in the same unit, they being of suitable reliability, therebyaffording assurance against the occurrence of plural simultaneousfailure or fault due to a common cause or inherent characteristic. Thus,similarly reserve batteries may be from a source different from those inoperation, or they may be from a different lot.

Further, it is remarked that the range for oxygen concentration (0.4-0.7atmosphere is regarded as particularly suitable for use under theconditions described herein, especially in relation to the diverbreathing equipment; however, such is revealing of the potential of thesystem rather than limiting upon the invention. The range and thecontrol point could, of course, be made variable by means obvious tothose skilled in the art. Moreover, the desired concentration may berelated and controlled according to any suitable voltage level.Additionally, the invention herein does not require that the oxygenlevel be held constantly near 0.5 atmosphere; rather, while such isdcsireable in the described embodiment, deviation therefrom may besubstantial, and then replenishment, may take place, such permitting,for example, the use of equipment involving a slower response to oxygendepletion and/or the applied signal. t

The expression signal failure" is used in the claims hereinafterpresented in a broad sense, and it is intended to refer to all possiblevariations of signal value from the normal gas concentrationproportional value, including the absence of a signal as would result,for example, from a dead sensor. The term spurious refers to a signalwhich is erroneous. either at a fixed or changing value, in relation togas concentration. As will be understood a spurious signal may degradeto the point of complete absence of a signal. In the course of such,however, it will have been limited in effect by the clipping circuitry.t t

We claim:

1. A closed circuit underwater breathing apparatus which maintains theconcentration of oxygen within a zone at or near a predetermined desiredlevel. which comprises at least three (3) separate means for sensingtheinstant oxygen concentration existing in said zone and for producingseparate signals normally proportional thereto, means for receiving saidthree signals and delivering thereupon a combined signal output normallysimilarly proportional to said concentration; oxygen supply controlmeans responsive to said output and operable to effect adjustment ofsaid oxygen concentration in said zone when said output deviates from avalue corresponding to said desired level; said device also includingmeans for controlling the effect of either of said separate signals uponsaid output in the event of an occurrence leading to a signal failure,whereby said output continues to be compatible with the operationalcharacteristics of said oxygen supply control means and saidconcentration is maintained substantially as normal notwithstanding suchoccurrence.

2. A closed circuit underwater breathing apparatus as claim in claim 1wherein said combined signal is an average of said three or moresignals, and including a separate physiologically compatible gas supplyfor internal pressure adjustment.

3. A device as claimed in claim 1 wherein metering means is provided foreach of said proportional signals.

4. A device as claimed in claim 3 wherein the said combined signal is anaverage of said three or more signals.

5. A device as claimed in claim 1 wherein warning means is provided togive notice of signal failure.

6. A device as claimed in claim 3 wherein warning means is provided togive notice of signal failure.

7. A device as claimed in claim 4 wherein warning means is provided togive notice of signal failure.

8. A closed circuit, self contained breathing apparatus comprising:

1. three or more oxygen sensor cells located in said closed circuitadapted to provide electrical signals proportional to oxygenconcentration;

2. separate means for amplifying eachof said signals;

3. separate indicator means responsive to each amplified signalproviding data in terms of oxygen partial pressure over the range ofzero to one atmosphere;

4. means for combining said amplified signals and delivering thereuponan average output proportional to said oxygen concentration, said outputcontrolling the input of oxygen via a solenoid operated valve andassociated circuitry such that said valve is closed at a predeterminedoxygen concentration falling within a preselected physiologicallytolerable oxygen concentration range and opens to deliver oxygen whensaid output represents an oxygen concentration below the saidpredetermined concentration;

5. electronic clipping circuitry effective to (a) limit the signal valueof any one of said three or more signals when their value reaches alevel corresponding to oxygen concentration at about the limits of oroutside the said preselected range, and (b) effect the inclusion of alimited signal value in said average which is not outside the range ofvalues corresponding to said predetermined range of oxygenconcentration;

6. audible alarm means connected in the electronic circuitry of saiddevice, said alarm being adapted to sound upon the limiting of anysignal value by said clipping circuitry;

7. manual means for depriving said valve of oxygen and means foreffecting the delivery of oxygen to said breathing circuit manually; and

8. diluent gas supply means connecting into said breathing circuit.

1. A closed circuit underwater breathing apparatus which maintains theconcentration of oxygen within a zone at or near a predetermined desiredlevel, which comprises at least three (3) separate means for sensing theinstant oxygen concentration existing in said zone and for producingseparate signals normally proportional thereto, means for receiving saidthree signals and delivering thereupon a combined signal output normallysimilarly proportional to said concentration; oxygen supply controlmeans responsive to said output and operable to effect adjustment ofsaid oxygen concentration in said zone when said output deviates from avalue corresponding to said desired level; said device also includingmeans for controlling the effect of either of said separate signals uponsaid output in the event of an occurrence leading to a signal failure,whereby said output continues to be compatible with the operationalcharacteristics of said oxygen supply control means and saidconcentration is maintained substantially as normal notwithstanding suchoccurrence.
 2. A closed circuit underwater breathing apparatus as claimin claim 1 wherein said combined signal is an average of said three ormore signals, and including a separate physiologically compatible gassupply for internal pressure adjustment.
 2. separate means foramplifying each of said signals;
 3. separate indicator means responsiveto each amplified signal providing data in terms of oxygen partialpressure over the range of zero to one atmosphere;
 3. A device asclaimed in claim 1 wherein metering means is provided for each of saidproportional signals.
 4. A device as claimed in claim 3 wherein the saidcombined signal is an average of said three or more signals.
 4. meansfor combining said amplified signals and delivering thereupon an averageoutput proportional to said oxygen concentration, said outputcontrolling the input of oxygen via a solenoid operated valve andassociated circuitry such that said valve is closed at a predeterminedoxygen concentration falling within a preselected physiologicallytolerable oxygen concentration range and opens to deliver oxygen whensaid output represents an oxygen concentration below the saidpredetermined concentration;
 5. electronic clipping circuitry effectiveto (a) limit the signal value of any one of said three or more signalswhen their value reaches a level corresponding to oxygen concentrationat about the limits of or outside the said preselected range, and (b)effect the inclusion of a limited signal value in said average which isnot outside the range of values corresponding to said predeterminedrange of oxygen concentration;
 5. A device as claimed in claim 1 whereinwarning means is provided to give notice of signal failure.
 6. A deviceas claimed in claim 3 wherein warning means is provided to give noticeof signal failure.
 6. audible alarm means connected in the electroniccircuitry of said device, said alarm being adapted to sound upon thelimiting of any signal value by said clipping circuitry;
 7. manual meansfor depriving said valve of oxygen and means for effecting the deliveryof oxygen to said breathing circuit manually; and
 7. A device as claimedin claim 4 wherein warning means is provided to give notice of signalfailure.
 8. A closed circuit, self contained breathing apparatuscomprising:
 8. diluent gas supply means connecting into sAid breathingcircuit.